Note: Descriptions are shown in the official language in which they were submitted.
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A DIRECT CURRENT TIGHT COUPLING
Background of the Invention
This invention relates to a direct current tight coupling
to connect two asynchronous hlgh-voltage three-phase power
systems.
To permit power exchange between two systems with
differing frequencies (asynchronous systems), one often uses an
isolated do circuit in the form of a three-phase--d.c.--
three-phase converter between the two power systems. Since the
h~gh-voltage do transmission taxes place practically at zero
distance, this do circuit is described as a do tight
coupling or a do short coupling.
Such a do tight coupling connecting two asynchronous
high-voltage power systems is described in the roster-
reichlsche Zeltschrlft fur Electrizltaetswirtschaft~ Austrian
Journal for the Electrical Industry), volume 36, issue 8/9,
pages 265 and following. It comprises primarily two
three-phase full-wave static converter assemblies,
interconnected on the do side and connected on the
three-phase side to both power systems, which, Instead of
having passive rectifier valves, contain controllable rectifier
components (thrusters). Thus is necessary because the power
exchange between the two coupled systems should selectively
occur in both directions. For that purpose, the static
converter unit allocated to the feeding power system has to
function as a rectifier, while the one allocated to the supply
network has to function as an inventor. As the mode of
operation thus only depends upon the polarity of the static
converter voltages, the transmission setup and the extent of
the energy flow are determined by the control of the system
exclusively and practically independent of the voltage and
frequency relationships in the connected three-phase power
systems. A prerequisite is the presence of a central thruster
electronic unit, wherein each thruster is allocated a
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thruster electronic subassembly consisting of an output unit
to generate and transmit an electronic ignition pulse as well
as an information processing electronic component and a signal
transfer unit. The signal transfer itself takes place by means
of photo conductor or fiber-optlc cables for a variety of
reasons which, however, are irrelevant to this particular
invention.
In the known high-voltage do tight couplings there are
always two static converter transformers each, of whose
secondary sides one is Wye-connected and the other
Delta-connected, operating onto a three-phase full-wave
rectifier with twelve semiconductor rectifier components. Each
phase of the three secondary three-phase circuits of both
static converter transformers is thus allocated two
semiconductor components connected in series so that four
semiconductor components form one semiconductor subassembly.
Each semiconductor component, in turn, consists of two
series-connected thrusters. These eight thyrlstors are
generally arranged one atop the other and together form a
occlude valve tower. The existing systems thus consist of a
total of six valve towers mounted in a so-called valve
housing. Each of these valve towers is connected on the arc.
side with one secondary phase connection each of the two
allocated static converter transformers and via a do bus each
with the two other valve towers allocated to the respective
power system.
Since the four static converter transformers are generally
mounted on the outside of the valve housing, two each to its
two longitudinal sides, and each of the two transformers has to
be connected by a line to each of the three valve towers, there
is a massive number of hlgh-voltage connecting fines crossing
each other, resulting in a correspondingly large spatial
requirement. In addition, each of the three ad~olnlng valve
towers of one power system has to be connected to the
corresponding thruster electronic unit using the already
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mentioned fibrotic cables. For that purpose special high-
voltage rated fiber-optic cables are used, whose range of
transmission is limited, however. Thus, for example, it is not
possible in the known arrangement to mount the transistor elect
ironic unit on one of the frontal sides off the valve housing at
the same level as the valve tower and transformers, because that
would exceed the maximum range of transmission of the fibrotic
cables. Designers were thus forced to create compartments beneath
the valve housing and to mount the thruster electronic unit
within those compartments to assure a short transmission path.
Accordingly, it will be appreciated that it would be highly
desirable to provide a more compact coupling arrangement, part-
ocularly of the semiconductor arrangement.
It is an object of this invention to provide a direct
current coupling for connecting two asynchronous high-voltage
power systems.
It is also an object of this invention to provide a
coupling which has a compact semiconductor arrangement.
Summary of the Invention
Briefly stated, in accordance with a broad aspect of
the present invention, there is provided a do tight coupling
for connecting two asynchronous high-voltage three-phase power
systems comprising a three-phase full-wave static converter
arrangement with static converter transformers and controllable
semiconductors allocated to each of the networks to be connected,
which are controlled by a central electronic control unit so that
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the input-side static converter assembly functions as an rectifier
and the output-side static converter assembly functions as an
inventor, with the controllable semiconductors of a functional
unit being arranged in a s-tack pattern forming matching static
converter towers connected on the do current side together at
the same pole and on the three-phase side with the respective Woe
and Delta-connected secondary sides of the static converter trays-
former: each of the full-wave semiconductor subassemblies
allocated to the four secondary sides of the static converter
transformers forming a static converter tower, wherein the four
static converter towers form a square pattern and are assembled in
such a manner that the static converter towers allocated to the
secondary sides of the static converter transformers of one power
system and the static converter towers assigned to the secondary
sides of the static converter transformers are located next to
each other parallel to the static converter towers, and the static
converter towers assigned to the Delta-connected secondary sides
of both power systems and the static converter towers assigned -to
the Woe connected secondary sides of both power systems face each
other.
This invention reduces the surface requirements of the
semiconductor towers by approximately one-third, while allowing
all three phases of each secondary side to be routed to one
single tower which eliminates the need for crisscrossing connection
lines. In addition, it means that the edge length of the surface
required by the static converter towers has been reduced to such
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a size that the thruster electronic unit can be mounted on one of
the frontal sides of the semiconductor housing at the same level
as are the semi-conductor towers. This eliminates the need for
the sub compartments of the static converter housing, thereby
substantially reducing the construction costs.
iffy Description of the Drawings
While the specification concludes with claims part-
ocularly pointing out and distinctly claiming the subject matter
which is regarded as the invention, it is believed that the
invention will be better understood from the following description
of the preferred embodiment taken in conjunction with the accom-
paying drawings in which:
Figure 1 is schematic diagram of the high-voltage do
tight coupling shown connecting two asynchronous high-voltage
power systems;
Figure 2 is a schematic illustration of the thrusters
of one power system assembled in two towers
Figure 3 is a simplified layout illustrating the stay
tic converter housing with static converter transformers, smoothing
reactors and thruster electronic control;
Figure 4 is a longitudinal cross sectional diagram of
the static converter housing with the soothing reactor and
thruster electronic control; and
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Fig. 5 is a longitudinal cross-sectlonal diagram, taken at
a fight angle to Fig. 4, of the static converts housing with
the static converter transformers.
Description off_ Preferred_Embodlment
Referring to Fig. 1, the three-phase open-wire fines of
the asynchronous three-phase power systems 1 and 2 which are to
be connected are first connected to the three-phase bus bars
3,4 of the coupling unit. Bus bar 3 is connected by connecting
lines 5 with the primary connections of the static converter
transformers 6 and 7, and the bus bar 4 is connected by
connecting lines 8 with the primary connections of static
converter transformers 9 and 10. Of the two static converter
transformers allocated to power system 1, the secondary side of
transformer 6 is Delta-connected, and the secondary side of
transformer 7 is reconnected The same applies for static
converter transformers 9 and 10 allocated to power system 2.
Each secondary phase connection is connected in the known
fashion to the three-phase connection of a three-phase
full-wave rectifier, each of which is equipped with 12
thrusters. The circuitry is known and requires no further
explanation. Both rectifier systems are directly connected Jo
each other by the grounded negative poles of the do voltage
side and by smoothing reactor 11 on the positive pole side.
In the known coupling arrangement four of the
series-connected thrusters of each of the three static
converter branches of each full-wave rectifier are stacked
above each other in four levels to form one so-called static
converter tower 12 shown by broken lines in Fig. 1.
Due to the symmetric design of the coupling system and the
use of thrusters in both full-wave rectifiers, one can select
the power-flow direction by a corresponding control of the
thrusters so that power either flows from system 1 to system 2
or vice versa. The energy flow direction can thus be selected
using a transistor electronic control. The static converter
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transformers 6, 7 or 9, 10, on the one hand, have the task to
transform the voltage of both three-phase systems to one
suitable for the static converters, and on the other hand, to
isolate the three-phase systems from the do circuit.
Smoothing reactor 11 serves, on the one hand, to reduce the
do ripples, but on the other hand to limit the short-circuit
current in case of thyrlstor short-clrcuits. By the
phase-gating control of the thrusters, harmonic waves are
created which can lead to voltage distortions in the
three-phase circuits and also cause interference with
communications circuits. In addition, these harmonic waves
produce an additional thermal load on transformers, capacitors
and transmission lines which are designed for a sinusoidal
current. It is thus necessary to remove the harmonic waves on
the three-phase side by high-pass filters 13, 14. As on the
do voltage side only active power can be transmitted, the
reactive power requirement on the three-phase side has to be
generated by capacitor batteries 15, 16.
As jig. 1 indicates, the combination of the four
thrusters connected in series to form one tower 12 assumes
that each tower is connected to one phase of the secondary side
of the three-phase circuit of each of the static converter
transformers allocated to a given power system. This results
in a relatively expensive crossing of long and thus expansive
connection cabling on the arc. current side. In addition, the
six static converter towers Require a relatively large mounting
surface which leads to the previously described problems when
connecting the control cables to the thyrlstors.
In this invention, therefore, the combination of the
static converters to form static converter towers is designed
differently. Specifically in this design, the four serially
connected static converters of a full-wave rectifier assembly
are not always assembled to form a tower; this design rather
combines the groups connected in parallel and formed by two
series connected thrusters which are allocated to each of the
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secondary sides of the static converter transformers. This
arrangement is depicted schematically in Fig. 2. wherein, the
left tower 18 includes the static converter subassembly of the
secondary Delta-side Lo', Lo', Lo' of static converter
transformer 6, and the right tower 19 includes that of the
secondary ye connection Lo, Lo, Lo of static converter
transformer 7. Each of the static converters shown in Fig. 1
correspond, in Fig. 2, to two identical thrusters 20 wired in
series with intervening reactors 21. The control connections
22 of the thrusters are connected to control lines (not shown)
which connect the thrusters to a thruster electronic unit.
In addition, for each two serially-connected thrusters there
is one control valve 23 connected in parallel to discharge
excess voltage. Fig. 3 illustrates the entire coupling
arrangement in schematic outline. The four static converter
towers 24, 25, 26, and 27 are arranged in a rectangular pattern
so that their three-phase connnectlons always face the assigned
static converter transformers 28, 29, 30, 31.
These transformers are located outside the static
converter housing 32 which encloses the static converter
towers. For that reason, relatively short non-crosslng
connecting lines can be used. In addition, the do current
buses 33, 34 and 35 connect the static converter towers
together as well as the lines 36, 37 feeding the smoothing
reactors 38 which are designed to assure the minimal possible
length and thus the greatest possible efficiency.
Since the edge length of the longitudinal side of the
static converter towers is now only two-thirds the length of
that previously obtained for the six-tower arrangement, the
thruster electronic control units 39, 40 can easily be mounted
at the same level as the towers and the transformers. The
length of the fiber-optlc connecting cables 41, 42 in this
arrangement is markedly shorter than the maximum possible
transmission length of such cables suitable for a high-voltage
environment.
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Fig. 4 illustrates the basic design configuration of the
static converter columns in a longitudinal section of the
static converter housing. This, once again, indicates success
in designing the feed and connecting lines both on the
three-phase side as well as on the do side in a short arid
clearly defined fashion. This is also clearly seen from the
cross-sectional view in Figure 5.
As will be evident from the foregoing description, certain
aspects of the invention are not limited to the particular
details of the example illustrated, and it is therefore
contemplated that other modifications or applications will
occur to those skilled in the art. It is accordingly intended
that the claims shall cover all such modifications and
applications as do not depart from the true spirit and script
of the invention.
